The use of digital image-forming apparatuses such as, for example, thermal ink-jet printers, large-format plotters, piezo-electric printers, large form plotters, laser printers, silver halide grade photo imaging apparatuses, and others has grown in recent years. The growth may be attributed to substantial improvements in print resolution and overall print quality coupled with appreciable reduction in cost, and ease of use. Today's image-forming apparatuses offer acceptable print quality for many commercial, business and household applications at costs lower than those offered in the past.
One of the challenges in inkjet printing is minimizing or controlling of bleed. Many inkjet inks, when printed in various colors on media (e.g., bond paper, copier paper), can lead to bleed. The term “bleed,” as used herein, is defined as the invasion of one color into another, once the ink is deposited on the print medium, as evidenced by a ragged border therebetween. Bleed occurs as colors mix either on the surface of the print medium (e.g., paper), within the print medium itself, within the deposited ink layer, or any combination of the preceding. The occurrence of bleed is particularly problematic between a darker ink (such as black ink) and an adjacently-printed lighter ink (such as yellow) because it is all the more visible.
To achieve improved bleed control, various approaches have been used, Prior solutions to reduce bleed have largely involved the use of heated platens or other heat sources and/or special paper. Heated platens add cost to the printer. Special paper limits the user to a single paper, which is of a higher cost than a “plain” paper. Other approaches have included increasing the penetration rate of the ink into the paper with the possible tradeoff of reduced edge acuity and/or color saturation, and/or the addition of a various additives to one or more inks. However, these additives typically have a deleterious effect on print quality and/or pen reliability, such as capped storage, kogation, decap, and waterfastness; as well as increased cost in custom designing inks within an ink set.
It would be desirable to provide printing inks for use in ink jet printers with improved bleed control, while allowing for greater flexibility in selection of the colorants.